Very few people even hit the current guidelines - with polls suggesting that 44 per cent of people in Britain do no regular exercise at all.Some 58 per cent of women and 65 per cent of men in England are either overweight or obese – a problem that is are expected to rise over the coming decades.

So health officials are focusing their efforts on getting people to exercise at all, rather than persuading them to spend hours and hours a week doing so.

That's the bottom line: if the target isn't realistic, many people won't bother at all.

"Maybe I will be my own inspiration." - UltraMonk (Laura)"Everywhere is walking distance if you have enough time." - Steven Wright

The fascinating thing for me was that the recommended amount is not based on what you need; but on what they think sedentary people might do. And, I'm glad my hours of "moderate" exercise is not that out of line with what is best.

(1) Watch for confirmation bias — we shoo away studies that go against what we currently do and embrace studies that align with our behavior

(2) Watch for vagueness — in a large meta-analysis like this, the specific categories and methodologies of the (nearly 200) individual studies don't line up and so "exercise" will necessarily have hard-to-define thresholds

(3) Watch for causation fallacies — while it's a plausible hypothesis, these studies don't actually prove that doing "X" amount of exercise (if you weren't already) will reduce your chance of getting various diseases by "Y" percent. Instead, it's about retroactive correlations. Perhaps certain subgroups of people who are intrinsically more prone to certain diseases are also less able to handle large amounts of exercise. Perhaps there is a third factor (e.g., a stressful job with very long hours) that influences both disease risk and exercise volume.

i wish media articles like this would include links to the actual studies when they report them - for those who want to read the actual source. anyway, good news is that the article is open access! http://www.bmj.com/content/354/bmj.i3857

there's a fairly lengthy list of limitations, most of which ian has summarized in plain english above. still, it's interesting to see the gap between the guideline and the evidence. like most policies, guidelines have to take into account more than just the evidence, and it makes sense to me here that, like la said, if most sedentary people heard that they "should" be getting 12 hours of exercise, they'd likely just throw in the towel. i don't know how the 150-minute guideline is worded, but maybe it would better to present a range from "minimum to ideal" minutes?

‘It is never too late to start and every little helps, with any ten minutes of physical activity improving your health

My first thought was that if someone is healthy enough to do 12 hours of exercise per week then genetics and other issues beyond their control may be the reason they are not having heart attacks, strokes and afflicted with cancer. So it is the classic chicken and egg question.

This also does not speak towards the quality of life. Does it make you happy or are you simply addicted to exercise. I do appreciate that those two things do not have to be mutually exclusive but it can get to a point where people start to suffer stress fractures, become isolated and depressed, etc, etc.

Everyone has different abilities and limits. I did what in theory and according to the article would provide me ideal health and I have a compression fracture with arthritis and exercise caused bradycardia to show for that. Thus I hold studies showing either minimums or maximums with a great deal of skepticism as they relate to the individual. Too much can be as bad or even worse then not enough. It reminds me of a recent study that had to be halted because a number of participants started to literally die. If memory serves it was to show the great benefit of anti-oxidation supplements. The theory was grand but the supplements were literally killing people.

I have come to a point in my life where the questions I ask I am having fun and I am healthy and not slowly wearing my body down and setting the stage for chronic issues. I have been forced into the realization that I am now at an age when a small and minor inconvenience can quickly turn into something much more serious and potentially permanent. I still want to challenge myself, even push myself out of my comfort zone. To ride 100 K in a single ride, I will need to work up to at least 70 or 80 K. Likewise, to run a marathon, enjoy it and minimize the heart damage risks, one has to run a certain minimal amount. But there is still being able to be smart about it, finding the right amount to allow one to still have fun and the wisdom to actually listen to your body when it firmly states that it cannot run as fast or as far or ... just to meet some arbitrary, subjective and at the end of the day, meaningless objective. Objectives can be fun, add spice but there is no reason why they cannot be kept in their proper perspective.